In electrical and optical data networks, data errors sometimes occur. When such problems are identified, the data transmission unit realizing a network node or terminating a transmission path must be tested. Here, the testing is performed by conventional protocol testers, which must be connected to the relevant data transmission unit, in particular, the receiver or transceiver units, which can be constructed as receiver or transceiver cards.
In known data transmission units, when such a test is performed, the data traffic frequently must be interrupted, because the test device must be connected to a port that is typically connected for further processing of the high bit-rate data signal by means of downstream electronics.
Therefore, a “service time window,” in which the relevant data traffic is shut down, must be provided by the operator of a data transmission network or a data transmission path. This usually takes place on the weekend and causes high administrative expense. In this “service time window,” the connection of the test device, the measurement, and the disconnection of the test device can then be performed.
In addition, there is the possibility of allowing the test equipment to also be connected during operation after its installation within a “service time window” and to disconnect the test equipment again when the error leading to the negative effect on the data transmission quality is found. For this purpose, a “service time window” must be created and used again.
In the case of an optical transmission path or an optical data transmission network, it is further known to integrate, for example, at the reception location, an optical splitter into the optical transmission path, wherein test equipment can be connected to the free arm of the splitter. This has the disadvantage, however, that an operator of a network or a data transmission path must already have invested in providing such splitters when the system is set up, and these splitters may never be needed. In addition, such a splitter has the disadvantage of corresponding insertion attenuation in the transmission path.
Finally, it is known to perform electrical mirroring of a high bit-rate data signal on a still free terminal of an interface, for example, a receiver or transceiver card, that is, the identical high bit-rate data signal that was received and optionally prepared with respect to the clock and the signal form is fed to this free terminal or output port of an interface.
In this known solution, the test device can be connected at arbitrary times to the relevant free terminal or output port of the appropriate interface. In this case, interrupting the data traffic is not necessary.
Here, however, it is disadvantageous that a data transmission device for realizing a network node or an end point of a transmission path frequently has a backplane, which possesses several plug-in positions for holding interface cards, for example, receiver or transceiver cards. In the way described above, if a “test output part” is provided on each interface, then each input port of the test device must be connected directly to the relevant free terminal of each interface, wherein testing a plurality of high bit-rate data signals on various interface cards is associated with high costs.